|
A Different VAWT design
|
|
By Dr Robert, Section Wind
Posted on Wed Dec 12, 2007 at 09:04:44 AM MST
|
My first 5 tries at making a low wind VAWT were not too good. But #6 and #7 were more related to a water turbine.
|
 |
I was recently introduced to Vertical Axis Wind Turbines (VAWTs) designs and I was definitely interested. Many bum steers later I came up with Prototype #7. It looked like a one cup Pelton Wheel on the inside but the outside was a Kaplan low head water turbine derivative!
The Pelton Turbine originally used nozzles to direct a high pressure streams of water directly into cups. I figured that if it worked for water, why not air somehow? Its the same thing except that water is 600 times more dense than air, right?.
On Prototype #6, I made eighteen long "cups" out of a pair of 10' long pieces of 4" white thin wall drain pipe PVC sawn longitudinally into two 180 degree semicircle lengths. I mounted the 18 lengths, each 28.5" long to my bicycle wheels revolving testbed. I turned on a pair of squirrel cage blowers and found it worked better than the previous models, and especially good if I directed both blowers directly into the cups. Good but not good enough.
I like to read biographical stories about inventors, so I read more about Pelton's invention. One day, Pelton noticed that his turbine was running faster for no apparent reason. Opening up the turbine, he discovered that one of the nozzles had come loose and was blasting the side of the cup instead of the middle.
This circulating motion was obviously imparting more power to the cups. I also read up on the trials and tribulations of Viktor Kaplan. He died disappointed in the performance of his invention. After Viktor's death, others discovered how its performance could be greatly improved. The Kaplan turbine gets its low head performance advantage from fixed blades that redirect the water directly into the rotating blades... I wondered??? In a hurry to try out an idea, I cut more 4" drainpipe PVC into eighteen 33.5" lengths of 90 degree quarter circles. I held these 90 degree pieces just outside of the arc subtended by the blades in #6, by inserting them into some scrap 2" styrofoam that I had lying around from another project.
Then I turned the squirrel cage blowers back on. WOW!!! The free running #7 was turning at triple the RPMs compared with #6 without the 90 degree pieces. It was Like what happened to Pelton. and it would start to run in a 1 MPH wind, not stopping until the wind dropped below 1/2 MPH.
It was time for theory to catch up with reality. When you look at a top down or bottom up 2D CAD view of VAWT #7, the answer becomes apparent. The 90 degree fixed pieces of PVC were acting like wind Circulators. They were redirecting the flow of the air 90 degrees. When the air exited the circulators, the upwind circulator air streams ran into the incoming air imparting a slight inward vector, resulting in a circulating stream of air significantly higher in velocity. This air ran into the inside edge of the 180 degree blades and wrapped around this inside edge imparting more energy just like Pelton had discovered. Looking at the 2D Cad model some more, the circulators on the windward side were not only blocking the wind from hitting the returning blades, but they were vectoring this blocked wind towards the powered side adding to the powered force. Because the circulators were effectively operating at a wider diameter than the blades themselves, they were acting like airscoops and were producing a venturi effect, giving the air another push in velocity. The downwind side circulators were also helping because they were causing a partial vacuum to appear on the exit point when the circulators forced a rapid expansion of the air when it exited the circulators.
Whew! At least that's what I think is making #7 look so good. To speed test, I have taken #7 on its 4' by 4' trailer out for a Spin (pun intended) on the local highway. Going down hill towards Denver, it looks like it is turning almost supersonic. In spite of the very light temporary construction used, there is no damage whatsoever caused by towing behind my car in the highly turbulent 55 mph wind. I tell the curious that it is part of an alien space ship. Keep watching along the highway for the rest of the space ship to come along soon.
From a distance the unit looks like a small round Carrier Air Conditioner, except it makes no noise even in a 55 MPH wind. It looks critter friendly especially when I put the wind screening cover over it soon. The wind screen will be made from perforated metal mesh used on old TVRO dishes. When a high velocity wind hits this perforated metal mesh, it dams up the holes and will vector around the VAWT, automatically saving the VAWT from high wind damage.
(I have also sent along 3 pictures but don't know how to attach them)
Robert |
|
|
Total Views
|
|
322 Scoop users have viewed this posting.
|
|
